It is known in vehicular test equipment to use gasoline engine spark plug electrical pulses as timing triggers for analysis of time-sensitive engine operations. Numerous events in spark-ignited gasoline engines, such as crankshaft angular position, engine rotation rate (generally referred to as RPM, the abbreviation for its units, revolutions per minute), valve timing, details of fuel flow and fuel injector function, and emission control functions are monitored or initiated using the firing time of a spark plug—typically the plug designated as “number one”—to trigger such test tools as a tachometer, a strobe light, or a modern processor-controlled multiple-function test instrument.
Spark events detected for triggering and analysis are commonly high-voltage pulses, appearing at, the secondary windings of stepup transformers, driving high-resistance wires to cause arcs to be formed at spark plugs. A variety of technologies have been developed to allow these potentially destructive pulses to actuate sensitive electronics, including resistive or capacitive voltage dividers that block all but a small fraction of the voltage; inductive clamps that use the current in the pulse to energize a miniature transformer temporarily installed around the spark plug wire; so-called Hall Effect probes that directly alter another electric current using the magnetic field associated with the current pulse; and other technologies of greater or lesser reliability and ease of use. Some of these technologies permit the waveform from the secondary winding to be evaluated in detail as an indication of the condition of the engine parts used for that pulse. With some technologies, it can be possible to identify faulty wires, stepup transformers (known in the art as coils), and coil primary circuits, as well as spark plug fouling and other phenomena, based on details of the secondary waveform.
Generating a trigger function for the monitoring of similar events in engines not dependent on spark plugs for initiating combustion, such as diesel engines, is a separate challenge. For diesel engines, ignition takes place spontaneously in the high compression environment of the cylinder with the piston at the proper location with respect to top-dead-center (TDC) after a charge of diesel fuel is injected into the cylinder. Operational testing and emissions testing requirements for diesels have become increasingly stringent, so improved ability to apply existing test apparatus to diesels is a growing demand.
Stand-alone testers exist that can detect one or another phenomenon associated with diesel operation and can generate electronic signals for such purposes as activating strobe lights for testing the timing relationship between crankshaft angle and fuel injection event. However, the greater capabilities associated with test equipment for spark-ignited gasoline-fueled engines are in general not available to the technician testing diesel engines.